Method of Surface Treatment and Surface-Treated Article

ABSTRACT

Plasma generated in water vapor bubbles present in a water-containing liquid is brought into contact, in the liquid, with an article having a contact angle with water of 90° or less. The plasma is contacted with an organic substance adhering to the article to thereby remove the organic substance from the article. By bringing the plasma into contact with the article, the surface of the article is etched without breaking the article. The article may comprise a material composed of both a hydrophobic part having a contact angle with water exceeding 90° and a hydrophilic part having a contact angle with water of 90° or less. In this case only the hydrophobic part is etched by bringing the plasma into contact with the article.

TECHNICAL FIELD

The present invention relates to a method of surface treatment of articles having a hydrophilic surface, and a surface-treated article by the method.

Priority is claimed on Japanese Patent Application No. 2005-089631 filed on Mar. 25, 2005, the content of which is incorporated herein by reference.

BACKGROUND ART

As a method for decomposing or removing organic substances by a plasma, for example, the following method is known.

(I) A method for removing organic substances which adhere to the surface of a substrate such as a silicon wafer or a glass substrate for liquid crystal by converting an oxygen gas or an argon gas into plasma under the atmospheric pressure, and spraying the plasma to the surface of the substrate has been proposed (see Patent Documents 1 and 2). Furthermore, an atmospheric pressure plasma surface treatment device has been put in practical use by this method and has been already manufactured.

(II) A method comprising irradiating ultrasonic wave to a liquid such as a organic solvent containing organic substances to generate bubbles in the liquid, irradiating electromagnetic wave to the bubbles to generate plasma in the bubbles, namely, generating plasma bubbles, and decomposing the organic substances dispersing in the liquid by the plasma bubbles has been proposed (see Patent Document 3).

(III) A technique for decomposing organic substances in water comprising supplying a gas such as oxygen and air into water to generate bubbles in water, applying a high voltage pulse to the bubbles so that the inside of bubbles becomes in a plasma state for a flash, and decomposing the organic substances in water by the plasma has been disclosed in Patent Documents 4 to 9.

(IV) A technique for imparting surface modification such as a portion consisting of alternate lands and grooves on the surface of fiber comprising generating plasma bubbles having high temperature in a liquid and adhering a compound generated from the plasma bubbles to the surface of the fiber, and a functionalized fiber obtained by the technique are disclosed in Patent Document 10.

According to the method (I), there are problems that (1) organic substances existed on the surface of a heat-resistant article such as an inorganic material can be decomposed or removed by plasma; however, the decomposed substances or unreacted organic substances float in the atmosphere; and (2) a high-energy plasma gas can be generated; however, it becomes difficult to apply to a polymeric organic material since the surface temperature of an article becomes extremely high.

According to the method (II), there are problems that (1) organic substances dispersed in the liquid can be decomposed; however, it is uncertain whether the method (II) can be applied for removing the organic substances adhered to the surface of an article; and (2) it is difficult to apply to a polymeric organic material since the surface temperature of the article becomes high, as well as the method (I), even if the plasma in the bubbles are contacted the article for decomposing the organic substances.

According to the method (III), there are problems that (1) organic substances dispersed in the liquid can be decomposed; however, it is uncertain whether the method (II) can be applied for removing the organic substances adhered to the surface of an article, as well as the method (II); and (2) since a plasma can maintain a plasma state for only a short time, it is difficult to effective decomposition when the frequency of contacting bubbles which is in plasma state (hereinafter, referred to plasma bubbles) and the organic substances to be decomposed is low.

The specification of Patent Document 10 of the method (IV) discloses that the surface modification of fibers can be carried out by contacting the plasma bubbles to the fiber. Raw materials of the fibers are not especially limited. However, as described in Patent Document 3 of the method (II), the plasma bubbles have high temperature of approximately 5000 K; on the other hand, the polymeric organic material does not usually have sufficient heat resistance which can withstand such high temperature. When a melting point and a softening point of the material are lower than the temperature of the plasma bubbles, it can be expected that the material will melt and flow, or will be thermal-decomposed or broken by contacting the plasma bubbles. It is difficult to apply the fiber using such material to the plasma bubbles. When such material having inferior heat resistance is used, it can be expected that the fiber itself will be destroyed rather than that the portion consisting of alternate lands and grooves will be imparted to the surface of the fiber. Furthermore, Patent Document 10 discloses a carbon fiber as an example; however, the carbon fiber is extremely thin and a part of the fiber which contacted the plasma bubbles being partially high temperature is excessively graphitized by heat though the degree of graphitization changes in accordance with the pattern of crinkles of the surface of the fiber, the level of graphite structure of the surface of the fiber, and the level of flame resistance. Therefore, it is considered that the fiber becomes brittle locally and mechanical properties of the fiber decreases as a whole. When the material having inferior heat resistance is used, Patent Document 10 does not disclose whether the fiber can be washed without changing the pattern of the surface thereof. As described above, Patent Document 10 does not disclose regarding election of material.

-   Patent Document 1: Japanese Unexamined Patent Application, First     Publication No. 2002-143795 -   Patent Document 2: Japanese Unexamined Patent Application, First     Publication No. 2004-311838 -   Patent Document 3: Japanese Unexamined Patent Application, First     Publication No. 2004-306029 -   Patent Document 4: Japanese Unexamined Patent Application, First     Publication No. 2005-502456 -   Patent Document 5: Japanese Unexamined Patent Application, First     Publication No. 2005-058887 -   Patent Document 6: Japanese Unexamined Patent Application, First     Publication No. 2005-021869 -   Patent Document 7: Japanese Unexamined Patent Application, First     Publication No. 2005-013858 -   Patent Document 8: Japanese Unexamined Patent Application, First     Publication No. 2004-268003 -   Patent Document 9: Japanese Unexamined Patent Application, First     Publication No. 2002-272825 -   Patent Document 10: Japanese Unexamined Patent Application, First     Publication No. 2005-105465

DISCLOSURE OF INVENTION Problems to be Solved by the Invention

An object of the present invention is to provide a method of surface treatment in which organic substances such as fouling which adheres to an article can be decomposed or removed without scattering in the atmosphere and damage of the article can be suppressed; a method for surface-treatment for etching the surface of the article with suppressing damage of the article; an article having little damage which is highly washed the surface thereof; an article having no damage which is etched by etching the surface thereof.

Means for Solving the Problems

A method of surface-treatment of the present invention is characterized by contacting, in a liquid containing water, plasma generated in water vapor bubbles in the liquid to a material in which a contact angle to water is 90° or less.

An article of the present invention is an article surface-treated by the above method of surface-treatment.

EFFECTS OF THE INVENTION

According to the method for surface-treatment of the present invention, the organic substances which adheres to an article can be decomposed or removed without scattering in the atmosphere and damage of the article can be suppressed. Furthermore, the surface of the article can be etched with suppressing damage of the article.

The article obtained by the method for surface-treatment of the present invention is highly etched or washed, and has little damage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of a plasma generating device.

FIG. 2 is a diagram showing a contact angle of water to the surface of an article.

FIG. 3 is a graph showing contact angle dependency of an etching speed by water vapor bubbles in the plasma state (hereinafter, referred to water vapor bubble plasma).

FIG. 4 is a typical diagram of a multilayer interconnection Damascene process.

FIG. 5 is a diagram showing emission spectrum from water vapor bubble plasma (Example 1).

FIG. 6 is electron microscope photographs of the surface of a hollow fiber membrane sample which is clogging.

FIG. 7 is electron microscope photographs of the surface of a hollow fiber membrane sample after treating the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

11 Liquid

12 Container

13 Electrode

14 Counter electrode

15 Article

16 Supports

17 Water vapor bubbles

18 Waterdrop

19 Air phase

γ_(SV) Surface tension of a solid which is in an adsorption equilibrium state to vapor of a liquid (water) (room temperature, atmospheric pressure)

γ_(SL) Interfacial tension of solid and liquid

γ_(LV) Surface tension of a liquid (water) which is in an equilibrium state to vapor (water-vapor)

BEST MODE FOR CARRYING OUT THE INVENTION

(Surface Treatment Method)

A method for surface-treatment of the present invention is a method of contacting, in liquid containing water, plasma generated in water vapor bubbles in the liquid to a material having hydrophilic surface. An index of a hydrophilic material in the present invention is a material having a contact angle to water being 90° or less.

As a plasma generating device used in the present invention, a plasma generating device disclosed in Japanese Unexamined Patent Application, First Publication No. 2003-297598 or Japanese Unexamined Patent Application, First Publication No. 2004-152523 may be used.

The method for surface-treatment of the present invention is explained by using a specific plasma generating device as an example as follows.

FIG. 1 is a schematic diagram showing an example of a plasma generating device which is used in the method for surface-treatment of the present invention. This plasma generating device 10 is equipped with a container 12 storing liquid 11, an electrode 13 for radiating electromagnetic wave which is provided in the container 12, a counter electrode 14 opposed to the electrode 13, supports 16 fixing an article 15 between the electrode 13 and the counter electrode 14, an electromagnetic wave power supply such as high-frequency power supply (not shown) connected to the electrode 13 and the counter electrode 14, and a vacuum pump (not shown) adjusting pressure of an air phase 19 (gas phase) which is placed over the liquid 11 of the container 12.

In the plasma generating device 10, the electrode 13 is connected to the electromagnetic wave power supply which can supply high frequency and high voltage. Since electromagnetic energy of this power supply is supplied to the electrode 13, the electrode 13 is heated, the liquid 11 around the electrode 13 is vaporized, and then water vapor bubbles 17 containing water vapor as a main component is adhered around the electrode 13.

If high frequency and high voltage are applied to the water vapor bubbles adhered to the electrode 13, molecular motion of water molecule in the bubbles is excited. Simultaneously, electron is emitted from atoms composing water molecule and a plus charge gas and electrons are generated. When a chain reaction in which the emitted electrons sequentially attack other water vapor generates, the plus charge gas and electrons are generated continuously and the inside of the water vapor bubbles becomes in the plasma state.

Light emission is shown in the specific wave range in the water vapor bubbles in the plasma state (hereinafter, referred to water vapor bubble plasma). The kind of gas generated in the plasma bubbles can be known from this emission spectrum. Table 1 shows a wavelength of the emission spectrum of the water vapor bubble plasma and the assignment of the kind of gas which is a light emitting component.

TABLE 1 Wavelength of emission spectrum (nm) Assignment of spectrum 306 OH-radical 434 Atomic hydrogen (H_(γ)) 486 Atomic hydrogen (H_(β)) 656 Atomic hydrogen (H_(α))

When the water vapor bubble plasma around the electrode 13 contacts a fouling composed of the organic substances adhered to the surface of the article 15 soaked in the liquid 11, the fouling is decomposed or removed by two actions, namely, (1) thermal decomposition by heat of the water vapor bubble plasma and (2) oxidization by OH-radical in the water vapor bubble plasma.

Though details are described later, in the surface treatment of the present invention, when the article has hydrophilicity, water being around the article is vaporized, the surface of the article is cooled by latent heat of vaporization, and therefore the thermal decomposition by heat of the water vapor bubble plasma as described (1) is decreased.

The liquid 11 may be used as long as a liquid contains water. Typical examples of the liquid 11 include water, an aqueous solution containing an organic solvent which can be mixed with water, and an aqueous solution in which an electrolytic ion is dissolved in water.

Examples of the organic solvent which can be mixed with water include alcohols such as methanol, ethanol, isopropyl alcohol, and butanol; and acetone. Examples of the electrolytic ion include Mg²⁺, Ca²⁺, Na⁺, Fe²⁺, Fe³⁺, Cl⁻, NO³⁻, NO²⁻, and OH⁻.

According to the electrolytic ion being in the liquid 11, electric conductivity of water is improved and arc discharge current tends easy to flow from the electrode 13 radiating electromagnetic wave to the counter electrode 14 when the plasma is generated. The organic solvent is carbonized by the plasma and the carbide may adhere to the article 15. If the volume fraction of water in liquid composition decrease, as described later, cooling effect by water to the surface of the article 15 decreases, and therefore, the surface of the article 15 becomes easy to be damaged. Therefore, preferably, the liquid 11 does almost not include the organic solvent, and more preferably, the liquid 11 does completely not include the organic solvent. Most preferably, pure water or ultrapure water which is used in a process for manufacturing a semiconductor is used.

The method for generating the water vapor bubbles 17 is not limited to the method of heating the electrode 13, but may be a method of providing an ultrasonic wave generating device, generating cavitation bubbles in the liquid 11 by ultrasonic wave from the ultrasonic wave generating device, vaporizing the ambient liquid 11 into the cavitation bubbles as vapor, and forming the water vapor bubbles 17.

The frequency of electromagnetic wave to be radiated to the water vapor bubbles 17 is selected according to its usage in the range of 1 MHz to 100 GHz.

The water vapor bubbles 17 may be generated by decompressing the air phase 19 in the container 12 by a vacuum pump. When the air phase 19 in the container 12 is decompressed, the boiling point of the liquid 11 decreases, water vapor becomes easy to generate, vapor pressure in the water vapor bubbles increases, and the number of water vapor molecules to be converted to plasma increases; as a result, plasma discharge is easily carried out. If the inside of the water vapor bubbles arrives in the plasma state once, plasma generation in the bubbles maintains even if the vacuum pump is stopped and the pressure of the air phase 19 is returned to an atmospheric pressure.

As the article 15, an article having a hydrophilic surface is preferred. Examples of the article 15 include a hydrophilic polymeric organic material, a glass, a ceramic, a silicon wafer, a metal (for example, aluminum, copper, tungsten, and the like), a graphite, and a carbon fiber.

In the present invention, the “hydrophilic surface” is defined by a value of contact angle θ defined in FIG. 2. The “hydrophilic surface” in the present invention is a surface having 90° or less of the contact angle θ of water (waterdrop 18) to the surface of the article 15 at 25° C. The contact angle of water to the hydrophilic surface is preferably lower, specifically 80° or less is more preferable and the range of 70° to 0° is most preferable.

The definition of the contact angle θ in the present invention is equal to that of the contact angle which is a usual index of wettability of a material to water. As a reference regarding the contact angle, the description of “Metallic Functional Surface”, written by Yukio Murakawa, published by Kindai Henshu-sya on 1984, pp. 133 is referred. According to the description, when a droplet is dropped to a smooth surface in which the droplet is not reacted with the surface, and the droplet is in the equilibrium state to the surface while keeping a certain contact angle, the following formula (1) is realized in FIG. 2.

γ_(SV)=γ_(SL)+γ_(LV) cos θ  (1)

γ_(SV) Surface tension of a solid which is in an adsorption equilibrium state to vapor of a liquid

γ_(SL) Interfacial tension of solid and liquid

γ_(LV) Surface tension of liquid which is in an equilibrium state to vapor

If the formula (1) is rewritten to the following formula (2), the left-hand side shows a decrease of a surface energy of the surface of solid which is wetted by liquid.

γ_(SV)−γ_(SL)=γ_(LV) cos θ  (2)

Since this energy is a surface free energy, wettability increases as the decrease amount of γ_(LV) cos θ becomes larger, i.e., wettability becomes better as θ becomes less if γ_(LV) has a constant value. The reason that the contact angle θ of the waterdrop is used for quantifying wettability is based on the formula (2). In the present invention, the liquid is water and γ_(LV) is 72.8 dyn/cm at 20° C. (see “Chronological Scientific Tables 1993” Maruzen Co., Ltd., pp. 449).

In the present invention, the contact angle θ in FIG. 2 is determined by preparing a material having a smooth surface, maintaining the surface horizontally, dropping a waterdrop to the surface, and measuring (θ/2) by a contact angle measure. If the surface of the material is porously or has a portion consisting of alternate lands and grooves, a smooth surface using the same material is prepared, and then the contact angle θ is determined. If the surface has a portion consisting of alternate lands and grooves in an organic polymer, a metal, a glass, or a ceramic, the smooth surface can be obtained by melting the same material. If the material is a material such as carbon fiber which cannot be melted, a smooth sheet consisting of a precursor raw material (for example, polyacrylonitrile or polyimide) is prepared beforehand, and subsequently the precursor raw material is calcined to obtain a sheet having the smooth surface consisting of carbon material. The contact angle is measured by dropping a waterdrop to this sheet. Examples of water used in the measurement of contact angle include clean water such as ultrapure water and ion-exchanged water.

Typical contact angles θ of water to the polymeric organic material and inorganic material at 25° C. are shown in Tables 2 and 3 (reference a: “Chemical Handbook, 4^(th) Edition, Basic II”, Maruzen Co., Ltd., 1993, II-83, 7.1.3 Contact Angle; reference b: “Wettability Technology Handbook” edited by Yoshio ISHII, Masazumi KOISI, and Mitsuo TUNODA, Techno Systems Inc., 2001, b1: pp. 418; b2: pp. 92; b3: pp. 96; b4: pp. 102-103; b5: pp. 161; and b6: pp. 198).

TABLE 2 Contact angle Polymeric organic material θ (degree) Polymer material (reference a) Nylon 6 61 Nylon 6,6 63-70 Nylon 11 75 Polyethylene 92-96 Polyvinylidene chloride 80 Polyvinyl chloride 83-87 Polystyrene 83-91 Polytetrafluoroethylene 108-113 Polytrifluoroethylene 92 Polychlorotrifluoroethylene 90 Polyethylene terephthalate 71-81 Polypropylene 95-98 Polymethyl acrylate 52 Polymethyl methacrylate 67-74 Polyethylene applied hydrophilic treatment Polyethylene film added lauryl alcohol (added 10 mol of 24 ethylene oxide) and triethanolamine phosphate Polyethylene film added lauryl alcohol (added 10 mol of 20 ethylene oxide) Polyethylene film added lauryl alcohol (added 10 mol of 22 ethylene oxide) and sodium phosphate

TABLE 3 Contact angle Inorganic material θ (degree) Graphite (reference b2) 82-86 Glassy carbon (reference b3) 90 Si(111) surface (include oxide film) (reference b4) 0-5 Si(111) surface (not include oxide film) Increase from (step of washing Si—OH surface by hydrofluoric acid to 10 to 80 change Si—H surface) (reference 4) Biocompatible material: hydro gel (reference b5) Polyhydroxyethyl methacrylate gel: water content 42% 10 Polyglycidyl methacrylate gel: water content 70% 15 Polyglycidyl methacrylate gel: water content 80% 10 Polyglycidyl methacrylate gel: water content 85% 10 Polyglycidyl methacrylate gel: water content 90% 10 Polyglycidyl methacrylate gel: water content 95% 10 Polyhydroxyethyl acrylate: water content 55% 15 Polyhydroxyethyl acrylate: water content 62% 22 Polyhydroxyethyl acrylate: water content 75% 20 Polyhydroxyethyl acrylate: water content 90% 20 Polyacrylamide: water content 62% 0-5 Polyacrylamide: water content 78% 5 Polyacrylamide: water content 86% 5 Polyacrylamide: water content 88% 5 Polyacrylamide: water content 92% 5 Biocompatible material: cellulose and polyvinyl alcohol (reference b6) Cellulose (cuprophan film): water content 51% 12 Polyvinyl alcohol film: water content 37% 38 Polyvinyl alcohol film: water content 73% 38

“Metal Surface Handbook” published by The Nikkan Kogyo Shimbun, Ltd., 1988, pp. 183 discloses that “the surface of a clean metal is wetted by water and the contact angle thereof is zero, and if there is a fouling part, wettability of the part decreases”. According to “Metallic Functional Surface”, written by Yukio Murakawa, published by Kindai Henshu-sya on 1984, pp. 134-136, the solid surface tension of γ-Fe is 1670 to 2127 dyn/cm according to results of the measurement in the molten state at high temperature and the solid surface tension of copper is approximately 1500 dyn/cm according results of the measurement in the molten state at high temperature, therefore, they are far larger than the surface tension of polymer. On the other hand, the surface tension of water is 72.8 dyn/cm. The surface of a clean metal is very easy to wet to water. The surface treatment of the present invention can be applied to a clean metal material having high surface energy.

In the present invention, any material such as a polymeric organic material, a glass, a ceramic, a metal, a graphite carbon material, a carbon fiber, and the like can be applied as long as the material satisfies θ≦90°.

When the wavelength of atomic hydrogen (H_(α): 656 nm) in plasma in the water vapor bubbles is converted into temperature, it is high temperature of approximately 5000 K. If the plasma gas having the above high temperature is contacted to an article consisting of a usual polymeric organic material, the article is completely destroyed at the instant of contact. The present inventors have found that when the article consisting of a hydrophilic material satisfying θ≦90°, only organic substances adhered to the surface of the article can be decomposed and removed, and subsequently washed without damaging the surface of the article, and the surface can be etched without destroying a clean article obtained by washing.

The idea of the present invention for overcoming thermal decomposition is schematically shown in FIG. 3. As shown in FIG. 3, if the contact angle θ to water of a material is 90° or less when the material is contacted to the water vapor bubbles, contribution of pyrolytic etching by heat is decreased, and if the contact angle θ to water of a material is larger than 90°, contribution of the pyrolytic etching is increased. The reason why this phenomenon occurs is described as follows.

The surface of the material satisfying θ being 90° or less is coated by a layer of water in liquid containing water. Even if the water vapor bubble plasma closes to the material, water on the surface of the material is vaporized while consuming latent heat of vaporization around the material and water is continuously supplied to the hydrophilic surface. Therefore, a persistent cooling effect is affected to the surface of the material and temperature rise of the article is suppressed. As a result, the surface temperature of the article does not exceed a heat-resistant temperature of the material, contribution of etching by thermal decomposition is decreased, and the damage of the material is suppressed. These effects are also effective for preventing local excess graphitization by heat of plasma in the surface treatment of carbon fiber.

It is known that when organic substances such as a fouling are adhered to the hydrophilic surface of the article, wettability of the hydrophilic surface changes to that of a hydrophobic surface. For example, according to “Wettability Technology Handbook” edited by Yoshio ISHII, Masazumi KOISI, and Mitsuo TUNODA, Techno Systems Inc., 2001, pp. 83-84, a pure metal surface is easily wetted, however, if the pure metal surface is left to stand in the atmosphere in which the organic substances exist, the organic substances gradually adhere to the metal surface and hydrophobicity of the metal surface increases with time. Simultaneously, the surfaces of hydrophilic organic material and ceramic also tend to become hydrophobic surfaces by contamination with organic substances.

According to FIG. 3, the fouling adhered to the surface of the material is decomposed by undergoing operations of thermal decomposition by heat of the water vapor bubble plasma and oxidative destruction by OH-radical. As the fouling decreases, a hydrophilic surface of the material appears and thermal decomposition is suppressed by cooling effect of water as described above, as a result, the surface of the material having little damage is obtained.

When the hydrophilic material having 90° or less of the contact angle is used, the material can be gradually etched by oxidative destruction by OH-radical while etching by thermal decomposition is suppressed. Various hydrophilic materials can be etched by the oxidative destruction. For example, a hydrophilic polymer material, a metal material, and a ceramic, or a glass showing hydrophilicity, a carbon material showing hydrophilicity, and the like can be etched.

In the surface treatment of the present invention, time during contacting the article 15 and the water vapor bubble plasma (hereinafter, referred to a contact time) may be adjusted suitably in consideration of heat-resistant temperature of the article 15, temperature in the bubble plasma, cooling effect of water generated on the surface of the article 15, and a degree of fouling.

If the contact time is too long, temperature of the surface of the material temporally exceeds the heat-resistant temperature by vaporizing water on the surface of the article 15 excessively until water to be existed on the surface of the article 15 becomes insufficient by the water vapor bubble plasma, or the article 15 is given a damage by a too strong oxidation of OH-radical.

If the contact time is too short, oxidation of OH-radical decreases, the surface of the article 15 tends to be insufficiently washed and etched.

The “contact time” in the present invention is defined as, if the article 15 rests, time during generating plasma in the water vapor bubbles 17 by applying voltage to the electrode 13 and the counter electrode 14, and if the articles 15 moves to a constant direction, the contact time is defined below.

Contact time (s)=Length (mm) in the movement direction in the range of generating plasma/Speed (mm/s) of movement of article 15

The index of the heat-resistant temperature of the material changes in accordance with kinds of materials. In the present invention, the heat-resistant temperature is defined as a temperature which is able to maintain the shape of the material.

In the polymeric organic material, the melting point in a crystalline material and the glass transition temperature in an amorphous are defined as indexes of heat-resistant temperature. Glass transition temperatures (Tg) and melting point (Tm) of typical crystalline polymeric organic materials are shown in Table 4 (Joel R. Fried, “Polymer Science and Technology”, Prentice Hall, 1995, pp. 140).

TABLE 4 Polymeric organic material Tg (° C.) Tm (° C.) High density polyethylene −120 135 Polycaprolactone −60 61 Polyvinylidene fluoride −45 172 Polyoxymethylene −85 195 Polyvinylalcohol 85 258 Nylon 6,6 49 265 Polyethylene terephthalate 69 265

In ceramics, a melting point is defined as an index of the heat-resistant temperature. Melting points (Tm) of typical ceramics are shown in Table 5 (Marcel Mulder, “Basic Principles of Membrane Technology, 2^(nd) Edition, Kluwer Academic Publishers, 1996, pp. 60).

TABLE 5 Ceramic Chemical formula Tm (° C.) Alumina Al₂O₃ 2050 Zirconia ZrO₂ 2770 Titania TiO₂ 1605 Silicon carbide SiC 2500

In optical glass materials, a grass transition temperature is defined as an index of the heat-resistant temperature. Glass transition temperatures of typical optical glasses are shown in Table 6 (Optical application technique workshop text, “Optical Material III-9”, Japan Optomechatronics Association, 1988, pp. 30).

TABLE 6 Kind of optical glass Tg (° C.) F2 432 BK7 565 SK16 648

In optical crystalline materials, a melting point is defined as an index of the heat-resistant temperature. Melting points (Tm) of typical optical crystalline materials are shown in Table 7 (Optical application technique workshop text, “Optical Material III-9”, Japan Optomechatronics Association, 1988, pp. 55).

TABLE 7 Optical crystalline Chemical material formula Crystal system Tm (° C.) Barium fluoride BaF₂ Cubic crystal 1280 Potassium bromide KBr Cubic crystal 748 Calcite CaCO₃ Trigonal crystal (Decomposed at 894° C.) Magnesium oxide MgO Cubic crystal 2800 Sapphire (ruby) Al₂O₃ Hexagonal crystal 2000 Quartz SiO₂ Hexagonal crystal <1470 Fused quartz SiO₂ (Amorphous) —

In metals, silicon wafers (silicon), and the like, a melting point is defined as an index of the heat-resistant temperature. Melting points (Tm) of typical metals are shown in Table 8 (“Chronological Scientific Tables 1993” edited by National Astronomical Observatory of Japan, published by Maruzen Co., Ltd., pp. 469).

TABLE 8 Metal Tm (° C.) Zinc 420 Aluminum 660 Gold 1064 Silver 962 Silicon 1414 Germanium 959 Zirconium 1852 Tin 232 Tungsten 3387 Graphite carbon 3550 Titanium 1675 Iron 1535 Copper 1085 Lead 328 Nickel 1455 Platinum 1772 Magnesium 651 Manganese 1244 Molybdenum 2610

In the carbon materials, since carbonization-graphitization has already progressed with time and it is difficult to determine a specific heat-resistant temperature, the melting temperature 3550° C. of a graphite single crystal of a related material is defined as an index of structural phase transition of the carbon material. The heat-resistant temperature of carbon fiber is defined to the temperature which can maintain the shape of fiber because there are many cases that the carbon fiber has low degree of crystallinity, a clear identification of amorphous parts and crystal parts is difficult, and the specific structural phase transition point of crystal is not easily determined.

(Application)

The surface treatment method of the present invention can be applied to (1) a washing step of an article in which organic substances such as a fouling are adhered (deposited) on the surface of the material, (2) an etching step of the surface of a hydrophilic material, and (3) a modifying step of imparting a portion consisting of alternate lands and grooves to the surface of the material.

The washing step (1) is explained below. Examples of the organic substances include general organic substances, which exist in daily living, such as a virus, bacteria, yeast, mold, algae, protozoa, protein, blood, and component of blood; animal or plant cells; organic substances contained in hair, domestic refuse, garbage, drainage, and the like; and a fertilizer component.

The following examples are listed as examples of washing articles according to the surface treatment method of the present invention. Objects of washing are not limited by the following examples, but any material can be selected as long as the article has hydrophilicity and the contact angle θ of water to the material is 90° or less. Furthermore, the article can be washed when a process is suitably selected according to temperature of the plasma bubbles and the cooling effect condition.

(a) A porous membrane is recycled by contacting plasma to the porous membrane having a hydrophilic surface used in a filtration treatment, and decomposing and removing filtration sediment consisting of the organic substances adhering to the surface of the membrane by thermal decomposition (or carbonization) or oxidation with OH-radical.

(b) A biocompatible material is recycled by contacting plasma to the biocompatible material having a hydrophilic surface which is taken out from a human body after the biocompatible material is embedded in the human body, decomposing and removing the organic substances adhering the surface of the biocompatible material by thermal decomposition (or carbonization) or oxidation with OH-radical. Examples of the biocompatible materials include polymethyl methacrylate resin, polylactic acid resin, polyurethane, hydrogel, cellose, polyvinyl alcohol, hydroxyapatite, and the like.

(c) Cancer cells in an organ are decomposed and removed by contacting plasma to the organ having a hydrophilic surface which is taken out from a human body to thermal-decompose (or carbonize) the cancer cells or oxidize the cancer cells with OH-radical.

(d) Organic substances such as protein adhering to a contact lens having a hydrophilic surface are decomposed and removed by contacting plasma to the contact lens to thermal-decompose (or carbonize) the organic substances or oxidize the organic substances with OH-radical.

(e) Bacteria adhering to a catheter or an artificial vascular graft having hydrophilic surfaces are eliminated by contacting plasma to the catheter or the artificial vascular graft before embedding in a human body, or organic substances adhering to a catheter or an artificial vascular graft having hydrophilic surfaces are decomposed and removed by contacting plasma to the catheter or the artificial vascular graft taken out from a human body to thermal-decompose (or carbonize) the organic substances or oxidize the organic substances with OH-radical. After decomposing and removing the organic substances, the catheter and the artificial vascular graft is disposed in safety.

(f) Organic substances adhering to the surface of a DNA sample detecting device having a hydrophilic surface are decomposed and removed by contacting plasma to the devise before or after using to thermal-decompose (or carbonize) the organic substances or oxidize the organic substances with OH-radical.

(g) Organic substances adhering to the surface of a non-woven fabric having a hydrophilic surface are decomposed and removed by contacting plasma to the non-woven fabric to thermal-decompose (or carbonize) the organic substances or oxidize the organic substances with OH-radical.

(h) A photoresist membrane is removed by contacting water vapor bubble plasma to the surface of a silicon wafer whose surface is coated by a lithography material such as the photoresist membrane. Or, a fouling on the silicon wafer is washed by contacting the water vapor bubble plasma to the silicon wafer in which the fouling adheres to the surface thereof.

(i) The surface of a glass plate, especially, a glass plate used for a liquid crystalline cell and the surface of a glass master used for a mastering process of an optical disk are required to be highly washed and cleaned. Conventionally, the RCA washing technique using a chemical solution is used. However, since the cost of drainage treatment of the chemical solution is charged extra, a washing technique without using the chemical solution is required. If the glass plate is washed using the technique of the present invention, a fouling adhering to the glass plate can be decomposed without impairing the surface of the glass plate by contacting OH-radical generated from the plasma bubbles to the glass plate and adjusting a contact time suitably. The decomposed substances become carbide, carbon dioxide, or water, and also toxic waste water is not generated.

(j) The fouling adhering to the surface of a ceramic product having a hydrophilic surface such as a Al₂O₃ ceramic tile is removed by washing using this technique.

(k) The surface of a photocatalytic tile product having a hydrophilic surface, which is coated by titanium oxide particles, is washed by the present technique. If the fouling is deposited on the surface of the photocatalytic tile product so that UV ray cannot arrive to the surface, the surface is washed to recover the photocatalytic property.

(l) The surface of a carbon electrode which is modified to have hydrophilicity is washed by the present technique. Especially, in a secondary battery using an electrolytic ion, a hydrophilic electrode is used if necessary. Repeating charging and discharging causes the electrolyte to be contaminated and a fouling is sometimes generated on the surface of the electrode. According to the present invention, the carbon electrode adhered with the fouling can be washed.

(m) A fluorine electrolytic membrane used for a solid electrolytic membrane (for example, Nafion® membrane manufactured by Du Pont) has high hydrophobicity. In this case, if the electrolytic membrane is soaked in water to swell the membrane by water, the water content of the membrane is increased and the contact angle to water is decreased. The surface of the membrane having 90° or less of the contact angle can be washed by the technique of the present invention.

Examples of the etching step of the surface of a hydrophilic material (2) as described above are as follows.

(n) The present invention can be applied to a Damascene process for removing an unnecessary metal film on a dielectric film by providing a groove on the dielectric film and embedding a metal film such as copper, aluminum, tungsten, titanium, and the like in a step of forming multilayer interconnection of semiconductor. FIG. 4 shows a schematic diagram of the Damascene process. In FIG. 4, a process is progressed by a b c and a patterning of a metal for wiring is formed in c.

Since the clean metal film has hydrophilicity as described above, the metal film can be precisely treated while the metal atom is removed with an atomic level by an electrochemical reaction of the metal atom and an atomic hydrogen and OH-radical generated from the water vapor bubble plasma. In this case, the speed of etching with OH-radical should be controlled suitably.

In Journal of the Japan Society of Precision Engineering, vol. 69, No. 9, 2003, pp. 1332-1336, Hidekazu Goto, Kikuji Hirose, Takashi Inada, and Yuzo Mori (Osaka University, Graduate School of Engineering, JPN) reported a new ultraprecise and ultrapure treatment method using a chemical reaction of an OH⁻ ion and a surface atom of a workpiece in which the OH⁻ ion is formed by dissociating a water molecule in ultrapure water to H and OH by a catalyst. If Al(001) is used for a cathode, they reported regarding a surface reaction elementary process that (1) if OH is bonded to the Al(001) surface atom, a binding affinity between the surface first layer and the second layer atom is decreases; and (2) if OH and H affect to a hydrogen-terminated Al(001) surface, all bonds between Al surface atoms are cut and the Al surface atoms are removed and treated as AlH₂(OH) molecules. In this document, H and OH are generated by the catalyst and an electrochemical reaction using the OH is used; however, any investigation result by OH-radical generated from the water vapor bubble plasma has not been disclosed. On the other hand, the present inventors emphasize that the present technique is applicable to a precise etching process for removing a metal from the material while chemical bonds of atoms of the metal surface are cut, as well as the above document, by affecting OH-radical generated from the water vapor bubble plasma of the present invention to the metal because a clear metal has hydrophilicity to water.

(o) Takeshi Hattori discloses, in “Electric Materials”, separate volume, December 2005, pp. 93-101, a washing technique of a silicon wafer. This document introduces a wet washing of a silicon wafer by washing the surface of the silicon wafer using RCA washing or a wet washing of the silicon wafer by washing by acid, alkali, dilute hydrogen fluoride aqueous solution, and ozone water while spinning the silicon wafer. On the other hand, using the technique of the present invention, the silicon wafer can be washed by OH-radical having stronger oxidation ability than the ozone water. According to “Improvement On Aquatic Environment By Means Of Discharge In Water Minute Bubble”, authored by Chobei Yamabe, fiscal year 2000-2002, Grant-in-Aid for Scientific Research, Report of Grant-in-Aid for Scientific Research (A) (2), March 2003, the standard oxidation potential of OH-radical is 2.84 eV and the standard oxidation potential of ozone is 2.07 eV, as a result, it is found that OH-radical has stronger oxidation ability than ozone.

Specifically, the silicon wafer can be washed by soaking a dirty silicon wafer in water of the reaction device shown in FIG. 1, and contacting the silicon wafer to the water vapor bubble plasma while rotating the silicon wafer.

A washing process for a porous membrane which is clogging after used for filtration as described in (a) is explained below as an example of a washing process for an article. Examples of porous membranes include a hollow fiber membrane made of polyethylene which is treated so as to be a hydrophilic one; a flat membrane; and a tubular membrane.

The dirty porous membrane is soaked in water and is anchored in the vicinity of an electrode radiating electromagnetic wave. If the electromagnetic wave is radiated from the electrode, water vapor bubbles are generated around the electrode, and simultaneously plasma is generated in the water vapor bubbles. If plasma generated in the water vapor bubbles is contacted to the surface of the porous membrane with a predetermined contact time, the organic substance adhering to the surface of the membrane is thermal-decomposed and blown out by plasma. The hydrophilic surface exposed after the organic substance is blown out is coated by a water layer because the hydrophilic surface tends to wet with water. As a result, the hydrophilic surface is hardly affected by plasma and a microporous structure formed by the porous membrane is almost completely maintained. The contact time is preferably 1 to 5 minutes. If the contact time is 1 minute or shorter, the organic substance such as a fouling adhering the surface of the porous membrane may be insufficiently removed. If the contact time is longer than 5 minutes, a part of the surface of the porous membrane starts melting. Specific examples of (a) are described above, and the same process can be applied to each example of (a) to (m) for removing the fouling. In addition, the present invention can be applied to each etching of (n) to (o).

The surface treatment method of the present invention is applicable to a partial etching of the article. That is, if the article having both the hydrophobic surface (θ>90°) and the hydrophilic surface (θ90°) is contacted to plasma, the speed of etching to the hydrophobic surface increases and a portion consisting of alternate lands and grooves is formed on the surface of the article.

For forming a surface having the portion consisting of alternate lands and grooves, it is necessary to select a contact time of a material and water vapor bubble plasma suitably.

This technique for forming the portion consisting of alternate lands and grooves is usable to etching of a material in a semiconductor lithography step, and a treatment process for forming a fine portion consisting of alternate lands and grooves of a plastic material (for example, a treatment process for imparting a non-glare function for preventing the reflection of an image to the surface of a transparent resin plate).

According to the surface treatment method of the present invention as explained above, since the surface of the article is contacted to the water vapor bubble plasma in a liquid, the decomposed organic substance from the article cannot be discharged into the atmosphere. Especially, without discharging virus, toxic organic substances, and the like into the atmosphere, they can be safely decomposed and removed in water. The decomposed substance can be safely extracted from water by collecting the decomposed substance which is transferred into water with an adsorption filter and the like. When articles used in a medical spot such as a hospital and a food manufacturing spot (for example, a catheter, an artificial vascular graft, a DNA sample detecting device, a non-woven fabric having a function of catching virus, a filter membrane for dialysis, a precision filter membrane, a gas separating membrane, and the like) are disposed, it is necessary to change the organic substances such as undesired bacteria adhering to the surface of the article, virus, and the like to the non-toxic substances safely. This object can be achieved by the present invention.

In etching of a material according to the surface treatment of the present invention, since OH-radical generated from water is used for decomposition without using an electrolytic solution or chemical agents such as sulfuric acid, hydrochloric acid, a hydrogen fluoride aqueous solution, and the like, waste water of the chemical agents is not generated after reaction. If the metal is etched, metal hydroxide is precipitated; however, since the metal hydroxide is insoluble to water, solid-liquid separation can be carried out, as a result, the toxic waste water to environment is not generated.

When the surfaced treatment using a carbon fiber suitable for the present invention is carried out, excessive graphitization by high temperature of the water vapor bubble plasma is suppressed and the surface treatment such as etching or washing by OH-radical to the whole fiber can be uniformly carried out while it is maintained that the fiber is stably carbonized. Therefore, the carbon fiber can be continuously manufactured; that is a high value-added manufacture industrially.

EXAMPLES Example 1

A water-purifying device for home use (trade name: Cleansui 02) manufactured by Mitsubishi Rayon Co., Ltd. was prepared. In a filtration cartridge of the water-purifying device, a hollow fiber membrane (the contact angel of water of a raw material which is treated so as to be a hydrophilic one (25° C.)=55°) made of polyethylene which was treated so as to be a hydrophilic one was used. The hollow fiber membrane is a hollow fiber membrane having inner diameter of 270 μm and thickness of the membrane of 55 μm manufactured by Mitsubishi Rayon Co., Ltd. In the hollow fiber membrane, fibrils made of polyethylene oriented in the direction of the fiber of the hollow fiber membrane, the hollow fiber membrane had a pore structure being a slit form in which many fibrils were piled up in the direction of the thickness of the membrane.

When the water-purifying device was set to a faucet of water supply in home, and water from water supply (Mikasa-cho, Iwakuni-shi, Yamaguchi-ken, Japan) was intermittently run through a filter cartridge for one year, the filter cartridge was clogged and the color of the surface of the hollow fiber membrane in the filter cartridge changed to pale gray. The filter cartridge was detached from the main body of the water-purifying device and active carbon was removed from the filter cartridge to obtain a clogged hollow fiber membrane sample. The surface of the clogged hollow fiber membrane was observed by an electron microscope. The electron microscope photographs are shown in FIG. 6. In the clogged hollow fiber membrane, slit-form pores on the surface of the membrane were clogged by organic substances.

The clogged hollow fiber membrane was washed by the following process.

Since the length of the clogged hollow fiber membrane sample was as short as 50 mm, the clogged hollow fiber membrane sample was fastened to a hollow fiber membrane which was treated so as to become a hydrophilic one (EX-540V polyethylene hollow fiber membrane manufactured by Mitsubishi Rayon Co., Ltd.) to prepare a sample for experiment.

As a plasma generating device, a device shown in FIG. 1 was used. As an RF power supply, type T161-5766LQ manufactured by Thamway Co., Ltd. was used, and as a matching box, type T0202-5766LQ manufactured by Thamway Co., Ltd. was used.

The sample for experiment was soaked in a container filled by water and the container was provided in the vicinity of the electrode and was fixed by supports. Water was heated using exothermic heat of the electrode, and water vapor bubbles were generated in water by heated water. In FIG. 1, at reduced pressure environment of 30 hPa of vapor pressure, the water vapor bubbles were irradiated with electromagnetic wave (27.1 MHz) at an output of 300 W so that water vapor in the bubbles became plasma state, and subsequently the pressure was adjusted to the atmospheric pressure for maintaining generation of the water vapor bubble plasma. An emission spectrum from the water vapor bubble plasma when the gas phase is at the atmospheric pressure is shown in FIG. 5. Spectrum intensity per wavelength of this emission spectrum was obtained by measuring light from the light-emitting bubbles using a PMA-11C-7473-36 Czeny-Turner type compact polychromator and a back-illuminated CCD linear image sensor both manufactured by Hamamatsu Photonics K.K. in the reaction device shown in FIG. 1. The number of light-detecting elements was 1024, the wavelength range was 200 to 950 nm, and exposure time was 19 ms. The measurement was carried out using a polychromator and a linear image sensor in which sensitivity unevenness of wavelength was adjusted and each wavelength axis was calibrated.

When the gas phase was in the state of the atmospheric pressure, the water vapor bubble plasma was contacted to the sample for experiment for three minutes. The surface of the hollow fiber membrane sample after surface treatment was observed by an electron microscope. The electron microscope photographs are shown in FIG. 7. The clogged organic substance was almost completely removed. Damage on the surface of the hollow fiber membrane was hardly observed and the pore structure was maintaining the original form.

Example 2

The same plasma generating device as Example 1 was used. The sample for experiment was soaked in a container filled with water and the samples were fixed with supports in the vicinity of the electrode. Except using an ethylene/vinyl alcohol copolymer film (hereinafter, may be referred to EVAL film) shown in Table 9 as a sample, water vapor bubble plasma was generated and the plasma was contacted to the sample for 3 minutes at the same condition as Example 1. Each film had the contact angle to water before contacting to plasma being within 64 to 71° and showed hydrophilicity. These films stood the heat of water vapor bubble plasma and maintained their original forms.

TABLE 9 Plasma durability⁶⁾ (Gas phase of reaction device: atmospheric pressure)⁷⁾ Measurement of contact angle of EVAL film Having durability⁸⁾: EVAL film good Ethylene¹⁾ θ/2²⁾ θ³⁾ RH⁵⁾ Not having Sample (mol %) (degree) (degree) T⁴⁾ (° C.) (% RH) durability⁹⁾: not good D2908 29 32.2 64.4 25.4 37 Good DC3203F 32 33.6 67.2 25.5 38 Good ET3803 38 34.6 69.3 25.6 38 Good AT4403 44 35.1 70.1 25.6 38 Good H4815B 48 35.7 71.4 25.7 38 Good ¹⁾Ethylene: ethylene content ²⁾θ/2: value observed by a contact angle measure CA-DT manufactured by Kyowa Surface Science, Co., Ltd. was used as the contact angle measure. The volume of drop of pure water was 1 μL. ³⁾θ: contact angle ⁴⁾T: temperature in a room for measurement ⁵⁾RH: humidity in a room for measurement ⁶⁾“Plasma durability” means durability of film to water vapor bubble plasma in water ⁷⁾“Gas phase of reaction device: atmospheric pressure” means that the gas phase placed over water of the container is composed of air having atmospheric pressure. The water vapor bubble plasma was generated in this state. ⁸⁾“Having durability” means that the original shape of the film was maintained without breaking. ⁹⁾“Not having durability” means that the film was decomposed after breaking by heat of plasma.

In the following Tables 10 and 11, the same symbols or terms as 1) to 9) have the same means.

The surface of the film of sample DC3203F was marked by oil-based ink. The marking part was irradiated with plasma, and as a result, the oil-based ink was decomposed by plasma and did not remain on the surface of the film. The film surface after washing was visually observed to be smoothly.

Example 3

Nafion® 112 and Nafion® 1035 membranes manufactured by DuPont were soaked in ion-exchanged water at 25° C. for 5 minutes to swell the membranes, and the swollen membranes were taken out and the contact angles thereof were measured. The contact angles were shown in Table 10. Nafion® 112 and Nafion® 1035 shown in Table 10 were used as samples for plasma treatment.

The same plasma generating device as Example 1 was used. The samples were soaked in a container filled with water and the samples were fixed with supports in the vicinity of the electrode. Subsequently, water vapor bubble plasma was generated at the same conditions as Example 1, and the plasma was contacted to the samples for 3 minutes. As shown in Table 10, both swollen Nafion® 112 and Nafion® 1035 membranes stood the heat of the water vapor bubble plasma, and their original forms were maintained.

TABLE 10 Plasma durability (Gas phase of reaction device: atmospheric pressure) Having durability: good θ/2 θ T RH Not having durability: Nafion ® membrane (degree) (degree) (° C.) (% RH) not good Nafion ® 112 34.3 68.5 26 38 Good After soaking in ion-exchanged water for 5 minutes Nafion ® 1035 38.2 76.5 25.9 38 Good After soaking in ion-exchanged water for 5 minutes

The surface of the Nafion® 112 membrane was marked by oil-based ink. The ink was firmly adhered to the membrane. The marking part was contacted to the water vapor bubble plasma in water for 3 minutes, and then the marking part was visually observed. The oil-based ink was decomposed by plasma and did not remain on the surface of the membrane. The surface of the membrane after washing was visually observed to be smoothly.

Example 4

The same plasma generating device as Example 1 was used. The sample for experiment was soaked in a container filled with water and the samples were fixed with supports in the vicinity of the electrode. Except using a glass plate which was optically polished (thickness: 5 mm, 100 mm×100 mm) as a sample, water vapor bubble plasma was generated and the plasma was contacted to the glass plate for 3 minutes at the same condition as Example 1. The glass plate stood the heat of water vapor bubble plasma and maintained its original form. The contact angle to water of the glass plate before contacting to plasma was approximately 35°.

Furthermore, the surface of the glass plate was marked by oil-based ink. The marking part was contacted to the water vapor bubble plasma in water for 3 minutes, and then the marking part was visually observed. The oil-based ink was decomposed by plasma and did not remain on the surface of the glass plate. The surface of the glass plate after washing was visually observed to be smoothly.

Example 5

The same plasma generating device as Example 1 was used. The sample for experiment was soaked in a container filled with water and the samples were fixed with supports in the vicinity of the electrode. Except using an alumina ceramic sheet (γ-Al₂O₃ sheet thickness: 3 mm, 100 mm×100 mm) as a sample, water vapor bubble plasma was generated and the plasma was contacted to the alumina ceramic sheet for 3 minutes at the same condition as Example 1. The alumina ceramic sheet after contacting stood the heat of water vapor bubble plasma and maintained its original form. The contact angle to water of the alumina ceramic sheet before contacting to plasma was approximately 55°.

Furthermore, the surface of the alumina ceramic sheet was marked by oil-based ink. The marking part was contacted to the water vapor bubble plasma in water for 3 minutes, and then the marking part was visually observed. The oil-based ink was decomposed by plasma and did not remain on the surface of the alumina ceramic sheet. The surface of the alumina ceramic sheet after washing was visually observed to be smoothly.

Example 6

The same plasma generating device as Example 1 was used. The sample for experiment was soaked in a container filled with water and the samples were fixed with supports in the vicinity of the electrode.

An ethylene-vinyl alcohol copolymer film (ethylene content: 32 mol %) was as a substrate (thickness: 3 mm, 100 mm×100 mm), a polyethylene film having 5 mm in width (thickness: 0.5 mm, 100 mm×100 mm) was adhered to the substrate with interval of 5 mm by heat seal to prepare a sample composed of a hydrophilic surface and a hydrophobic surface (hydrophilic part: 5 mm in width, hydrophobic part: 5 mm in width). The contact angle to water of the ethylene-vinyl alcohol copolymer film was 67° and the contact angle to water of the polyethylene film was 95°.

Except using the prepared sample, water vapor bubble plasma was generated and the plasma was contacted to the whole sample for 3 minutes by the same method as Example 1. After contacting, when the sample was taken out from a reaction container, the polyethylene film which was the hydrophobic part was etched by plasma and then the average thickness thereof was 0.1 mm. On the other hand, the ethylene-vinyl alcohol copolymer film substrate was maintained the original smooth surface. Only hydrophobic part was etched by plasma.

Comparative Example 1

As articles, a polytetrafluoroethylene film having 100 μm thickness in which hydrophilic treatment was not carried out (contact angle to water (25° C.): 110°), a polyethylene film (contact angle to water (25° C.): 95°), and a polypropylene film (contact angle to water (25° C.): 96°) were prepared. The surfaces of these films were not adhered with organic substances such as fouling. The surface treatment was carried out to these films using the same method as Example 1. The moment plasma was contacted to these films these films were thermal-decomposed by high temperature of plasma and were broken.

Comparative Example 2

As articles, a polymeric organic porous flat membrane having 50 μm thickness in which hydrophilic treatment was not carried out (manufactured by Nihon Millipore K.K., hydrophobic polytetrafluoroethylene membrane, contact angle to water (25° C.): 110°, average pore size: 1 μm), and a polymeric organic porous flat membrane having 100μm thickness (manufactured by Nihon Millipore K.K., hydrophobic polyethylene membrane, contact angle to water (25° C.): 94°, average pore size: 1 μm) were prepared. The surfaces of these polymeric porous flat membranes were not adhered with organic substances such as fouling. The surface treatment was carried out to these polymeric porous flat membranes using the same method as Example 1. The moment plasma was contacted to these flat membranes these flat membranes were thermal-decomposed by high temperature of plasma and were broken.

Comparative Example 3

Except using two kinds of Nafion® membranes (Nafion® 112 and Nafion® 1035) manufactured by DuPont which were left to stand at 25° C. and 55% RH for one week as samples, the water vapor bubble plasma was contacted to the samples at the same condition as Example 3.

The contact angles to water of Nafion® 112 and Nafion® 1035 before contacting to plasma were shown in Table 11. The moment plasma was contacted to these membranes both Nafion® membranes were thermal-decomposed by high temperature of plasma and were broken.

TABLE 11 Plasma durability (Gas phase of reaction device: atmospheric pressure) Having durability: good Nafion ® θ/2 θ RH Not having durability: not membrane (degree) (degree) T (° C.) (% RH) good Nafion ® 112 46.6 93.2 26 38 Not good Initial state Nafion ® 47.3 94.7 25.9 38 Not good 1035 Initial state

Comparative Example 4

200 mL of pure water was prepared in a 300 mL volume beaker, the clogged hollow fiber membrane used in Example 1 was soaked in pure water of 25° C., and the hollow fiber membrane was washed by a 20 KHz ultrasonic washer with output of 100 W for one hour. The washed membrane was observed by an electron microscope. The organic substance clogging in the membrane surface was not removed.

Comparative Example 5

In Example 1, the electrode in the reaction device was heated to generate water vapor bubbles not in the plasma state and the water vapor bubbles were contacted to the clogged hollow fiber membrane sample for 3 minutes. As a result, the organic substance clogging in the membrane surface was not removed.

INDUSTRIAL APPLICABILITY

The present invention is a surface treatment method for decomposing and removing organic substances adhering to an article by contacting plasma generated in water vapor bubbles and the article having a hydrophilic surface without injuring the article. This surface treatment method is usable to, for example, a water-purifying device for home use, a filter for industrial wastewater, a polymeric organic porous membrane for an air filter, recycle of a ceramic porous membrane, and safety disposal of a porous membrane. Especially, the surface treatment method is usable to a method for safety recycling or disposing membranes contaminated or clogged by a substance containing bacteria such as a membrane filter for water of lavatory in a hospital, a membrane air filter for preventing hospital infection in hospital, a membrane air filter for a biohazard safety room, and the like.

The surface treatment method of the present invention is applicable to a treatment for safety disposing a biocompatible material by thermal-decomposing or carbonizing organic substances such as bacteria on the surface of the material after embedding the biocompatible material in a human body and using the material; a treatment for using for safety of a life by thermal-decomposition or carbonizing cancer cells coexisting with organs; a treatment for safety disposing spent contact lenses by thermal-decomposing or carbonizing organic substances such as bacteria, blood, and protein adhering to the lenses; and the like. Furthermore, the surface treatment method of the present invention is also applicable to a treatment for eliminating bacteria from a catheter, an artificial vascular graft, and the like before being embedded in a human body and sterilizing bacteria and the like adhering to the catheter, artificial vascular graft, and the like after being taken out from the human body; a treatment for removing bacteria which is not an object of detection from a DNA sample detecting device; a treatment for safety disposing the spent DNA sample detecting device; a treatment for safety disposing an air filter, a mask, and the like in which non-woven fabric is used by thermal-decomposing or carbonizing bacteria adhering to the non-woven fabric; and the like.

The etching process of the present invention is usable for processing a privacy filter in which antireflection function for optical use and visibility at only specific view angle are developed by imparting a portion consisting of alternate lands and grooves finely to the surface of a hydrophilic transparent organic material. Furthermore, the surface of a metal film can be etched by a chemical species derived from a water molecule. As a result, since the cost of disposing treatment can be decreased in a Damascene process of high density multilayer interconnection in a semiconductor device, the present invention is effective for the decrease of manufacturing cost.

For the semiconductor multilayer interconnection device, in recent years, high density interconnection and a more fine processing are required. In this case, a material having low dielectric constant made of porous silicon membrane has been proposed as a dielectric film. Since this dielectric film has large pore volume and the material of the film has a hydrophobic contact angle to water, it is difficult to flatten the whole after etching a metal film in a conventional chemical mechanical polishing process because a polishing solution is repelled by the dielectric film. On the other hand, according to the process of the present invention, if a material having a contact angel to water of 90° or less is selected as a low dielectric constant film, the low dielectric constant film is etched by OH-radical in the water vapor bubble plasma and a structure of a flat dielectric film/a multilayer interconnection metal can be obtained.

According to the etching process of the present invention, if the contact time to the water vapor bubble plasma is controlled to be short, only a hydrophobic part can be selectively etched. This method is applicable to a selective etching process of the hydrophobic part in various materials such as an organic material, an inorganic material, and a carbon material containing both hydrophilic surfaces and hydrophobic surfaces. Especially, though the surface treatment of materials such as the carbon material and a silicon wafer is difficult because the materials have a high heat-resistant temperature, the etching becomes easily according to the etching process of the present invention. 

1. A method of surface treatment comprising: contacting plasma generated in water vapor bubbles in a liquid comprising water to a material having a contact angle to water of 90° or less in the liquid.
 2. An article surface-treated by the method of surface treatment according to claim
 1. 3. A method of surface treatment comprising: contacting plasma generated in water vapor bubbles in a liquid comprising water to organic substances adhering to a material having a contact angle to water of 90° or less in the liquid comprising water to remove the organic substances.
 4. The method of surface treatment according to claim 3, wherein the material having a contact angle to water of 90° or less is a polymer porous membrane.
 5. The method of surface treatment according to claim 3, wherein the material having a contact angle to water of 90° or less is a polymer electrolytic membrane.
 6. The method of surface treatment according to claim 3, wherein the material having a contact angle to water of 90° or less is a glass.
 7. The method of surface treatment according to claim 3, wherein the material having a contact angle to water of 90° or less is a ceramic.
 8. An article surface-treated by the method of surface treatment according to claim
 3. 9. An etching process comprising: contacting plasma generated in water vapor bubbles in a liquid comprising water to a material having a contact angle to water of 90° or less in the liquid comprising water to etch a surface of the material without breaking.
 10. The etching process according to claim 9, wherein the material having a contact angle to water of 90° or less is a metal.
 11. The etching process according to claim 10, wherein the metal is at least one selected from the group consisting of copper, aluminum, and tungsten.
 12. An article etched by the etching process according to claim
 9. 13. An etching process comprising: contacting plasma generated in water vapor bubbles in a liquid comprising water to a material comprising both a hydrophobic part having a contact angle to water of more than 90° and a hydrophilic part having a contact angle to water of 90° or less in the liquid comprising water to etch the hydrophobic part.
 14. An article etched by the etching process according to claim
 13. 